(a) Field of the Invention
The present invention relates to an improved method for preparing an aromatic secondary amino compound. The present invention also relates to an improved method for the preparation of aminodiphenylamine.
The aromatic secondary amino compound obtained by the method of the present invention is an extremely important industrial chemical such as a raw material for rubber chemicals, dyes and the like.
(b) Description of the Prior Art
As methods for preparing an aromatic secondary amino compound, there are known a method in which the reaction of toluidine is carried out in a liquid phase at 300.degree. to 400.degree. C. in the presence of a suitable self-condensation type reaction catalyst (BF.sub.3, FeCl.sub.2, a salt of an ammonium halogenide, or a mineral acid), and a method in which cresol is reacted with toluidine at 330.degree. to 340.degree. C. under pressure in the presence of triphenyl phosphate.
Other methods for preparing the aromatic secondary amino compound are also known which comprise the dehydrogenation reaction of an N-cyclohexylideneamino compound. For example, there are a method for obtaining N-cyclohexylidene-N'-isopropylphenylenediamine at a temperature of 350.degree. C. or less in the presence of a dehydrogenation catalyst (British Patent No. 989257); a method in which reaction is carried out in a gaseous phase, while oxygen or an oxygen-containing gas is fed at 300.degree. to 450.degree. C. in the presence of an oxidizing catalyst such as silica or alumina (Japanese Patent Application Laid-open No. 49924/1974); a method for obtaining 4-methyldiphenylamine by reaction at 300.degree. to 500.degree. C. in the presence of a dehydrogenation catalyst selected from the group consisting of nickel, platinum, palladium and copper-chromium alloy (Japanese Patent Application Laid-open No. 49925/1974); and a method for preparing an amino compound by the use of a specific nickel/chromium catalyst (Japanese Patent Publication No. 4623/1982).
Still other methods are already known in which a nitro compound is used as a hydrogen acceptor in the presence of a hydrogen moving catalyst to produce an amine in the system, and a nucleus-substituted cyclohexanone is simultaneously reacted with the amine to prepare an aromatic secondary amino compound. For example, there are a method for obtaining p-ethoxydiphenylamine by reacting p-nitrophenetole with a large excess of cyclohexanone in the presence of a palladium catalyst (British Patent No. 975097); a method for obtaining 2,6-dimethyldiphenylamine by reacting 1/3 mol of 2,6-dimethylaniline, 2/3 mol of 2,6-dimethylnitrobenzene, and cyclohexanone in the presence of a palladium catalyst, the amount of cyclohexanone being 10% in excess of the total of 2,6-dimethylaniline and 2,6-dimethylnitrobenzene (British Patent No. 989257); and a method for preparing a diphenylamine derivative by reacting 2 -(alkyl or alkoxy)-4-alkoxynitrobenzene, 2-(alkyl or alkoxy)-4-alkoxyaniline and cyclohexanone in the presence of a palladium catalyst (Japanese Patent Application Laid-open No. 117214/1993).
However, these conventional methods have drawbacks of (1) severe reaction conditions, (2) a low reaction rate, and (3) a low yield. For these reasons, they are not industrially satisfactory manufacturing methods.
Known preparation processes of 4-aminodiphenyl-amine include rearrangement and reduction of N-nitroso-diphenylamine obtained by nitrosation of p-phenylenediamine (P.B. Reports 77764, 27-32) and condensation of formanilide or acetanilide with a halonitrobenzene, followed by reduction of the nitro group [Journal of Organic Chemistry, 42(10), 1786-90]. Known preparation processes of 2-aminodiphenylamine include rearrangement of an azo compound [Journal of Organic Chemistry, 295(1), 91-7, 1985]. Further, known preparation processes of 3-aminodiphenylamine include reduction of 3-nitrodiphenylamine. They are however hardly considered as industrially advantageous processes, because they require a complex reaction step, a large amount of a special reagent and/or solvent, and/or a precise purification step.
It is also known, as in the further aspect of the present invention, to prepare aminodiphenylamine by reacting cyclohexanone and phenylenediamine in the presence of a hydrogen transfer catalyst and a hydrogen receptor. Pursuant to this process, aminodiphenylamine has been obtained by reacting cyclohexanone and phenylenediamine in the presence of a palladium catalyst while using .alpha.-methylstyrene as a hydrogen receptor (Japanese Patent Laid-Open No. 58648/1982). In this process, however, except for its use as a hydrogen receptor, .alpha.-methylstyrene cannot effectively be used for the reaction, in contrast with the hydrogen receptor in this further aspect of the present invention, and phenylenediamine as a raw material has to be supplied in its entirety into the reaction system in the form of phenylenediamine. The reaction has to be conducted at elevated temperature and pressure. This process is therefore hardly considered to be satisfactory as an industrial process.